Heart failure is highly prevalent in many countries in the world and is the primary reason for hospital admissions. A major complication for patients with moderate-to-severe heart failure is accumulation of excess fluids in the lungs. Excess lung fluid is a frequent cause of hospital re-admissions. In fact, it has been reported that by the time excess lung fluid is detected, it is often too late to avert hospitalization.
Previously proposed methods of lung fluid detection include the use of X-ray imaging, CT scan (of the thorax), and measurement of serum biomarkers (e.g. Brain Natriuretic Peptide). These methods are sophisticated and can involve the use of bulky equipment or can take a long time to produce a measurement, thus making them impractical for use during an emergency or outside a hospital environment.
A less sophisticated and faster method of assessing accumulation of excess lung fluid is for a physician to perform auscultation (i.e. listening for audible evidence of fluid accumulation) using a stethoscope. However, while quicker and simpler, this method lacks the sensitivity of the more sophisticated methods discussed above.
A more recent development is a device which can be implanted in order to continuously monitor the fluid status of the lungs, for example by measuring intrathoracic impedance. Although this may advantageously allow earlier detection of fluid accumulation, implantation is an invasive procedure.
There is a need for a non-invasive approach to the detection of fluids in internal organs such as lungs.